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From: Segher Boessenkool <segher@kernel.crashing.org>
To: Borislav Petkov <bp@alien8.de>
Cc: "Arvind Sankar" <nivedita@alum.mit.edu>,
	"Jakub Jelinek" <jakub@redhat.com>,
	jgross@suse.com, x86@kernel.org,
	"Kees Cook" <keescook@chromium.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	linuxppc-dev@lists.ozlabs.org, "Michael Matz" <matz@suse.de>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"Sergei Trofimovich" <slyfox@gentoo.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Paul Mackerras" <paulus@samba.org>,
	"Andy Lutomirski" <luto@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Frédéric Pierret (fepitre)" <frederic.pierret@qubes-os.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Martin Liška" <mliska@suse.cz>,
	boris.ostrovsky@oracle.com
Subject: Re: [PATCH] x86: Fix early boot crash on gcc-10, next try
Date: Sat, 25 Apr 2020 13:37:01 -0500
Message-ID: <20200425183701.GE17645@gate.crashing.org> (raw)
In-Reply-To: <20200425173140.GB24294@zn.tnic>

On Sat, Apr 25, 2020 at 07:31:40PM +0200, Borislav Petkov wrote:
> > There's also the one in init/main.c which is used by multiple
> > architectures. On x86 at least, the call to arch_call_rest_init at the
> > end of start_kernel does not get tail-call optimized by gcc-10, but I
> > don't see anything that actually prevents that from happening. We should
> > add the asm("") there as well I think, unless the compiler guys see
> > something about this function that will always prevent the optimization?
> 
> Hmm, that's what I was afraid of - having to sprinkle this around. Yah, let's
> wait for compiler guys to have a look here and then maybe I'll convert that
> thing to a macro called
> 
> 	compiler_prevent_tail_call_opt()
> 
> or so, so that it can be sprinkled around. ;-\

That is a lot more typing then
	asm("");
but more seriously, you probably should explain why you do not want a
tail call *anyway*, and in such a comment you can say that is what the
asm is for.

I don't see anything that prevents the tailcall in current code either,
fwiw.


Segher

  parent reply index

Thread overview: 79+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-14 16:44 [PATCH] x86: fix early boot crash on gcc-10 Sergei Trofimovich
2020-03-16 13:04 ` Peter Zijlstra
2020-03-16 13:26   ` Jakub Jelinek
2020-03-16 13:42     ` Peter Zijlstra
2020-03-16 17:54       ` Borislav Petkov
2020-03-16 18:03         ` Jakub Jelinek
2020-03-17 14:36           ` Borislav Petkov
2020-03-17 14:39             ` Jakub Jelinek
2020-03-17 14:49               ` Borislav Petkov
2020-03-17 16:35                 ` David Laight
2020-03-25 13:31                 ` Borislav Petkov
2020-03-26 21:54                   ` Sergei Trofimovich
2020-03-26 22:35                     ` Borislav Petkov
2020-03-28  8:48                       ` [PATCH v2] " Sergei Trofimovich
2020-04-13 14:15                         ` [tip: x86/urgent] x86: Fix " tip-bot2 for Sergei Trofimovich
2020-04-13 16:35                         ` [PATCH v2] x86: fix " Borislav Petkov
2020-04-14 13:50                           ` Michael Matz
2020-04-15  7:48                             ` Borislav Petkov
2020-04-15 14:53                               ` Michael Matz
2020-04-15 22:19                                 ` Sergei Trofimovich
2020-04-17  7:57                                   ` Borislav Petkov
2020-04-17  8:07                                     ` Jakub Jelinek
2020-04-17  8:42                                       ` Borislav Petkov
2020-04-17  8:58                                         ` Jakub Jelinek
2020-04-17  9:09                                           ` Borislav Petkov
2020-04-17 18:15                                             ` Nick Desaulniers
2020-04-17 18:22                                               ` Nick Desaulniers
2020-04-17 19:06                                                 ` Jakub Jelinek
2020-04-17 19:49                                                   ` Nick Desaulniers
2020-04-17 19:53                                                     ` Nick Desaulniers
2020-04-20 14:04                                                     ` Michael Matz
2020-04-22 10:23                                                       ` Borislav Petkov
2020-04-22 11:40                                                         ` Peter Zijlstra
2020-04-22 13:49                                                           ` Borislav Petkov
2020-04-22 13:55                                                             ` Jakub Jelinek
2020-04-22 14:16                                                               ` Martin Liška
2020-04-22 15:06                                                                 ` Michael Matz
2020-04-22 16:53                                                                 ` Borislav Petkov
2020-04-22 17:02                                                                   ` Jakub Jelinek
2020-04-22 18:47                                                                   ` Nick Desaulniers
2020-04-22 18:55                                                         ` Nick Desaulniers
2020-04-22 19:21                                                           ` Borislav Petkov
2020-04-22 21:05                                                             ` Nick Desaulniers
2020-04-22 21:26                                                               ` Borislav Petkov
2020-04-22 22:57                                                                 ` Nick Desaulniers
2020-04-23 12:53                                                                   ` Borislav Petkov
2020-04-23 16:12                                                                     ` [PATCH] x86: Fix early boot crash on gcc-10, next try Borislav Petkov
2020-04-23 17:30                                                                       ` Borislav Petkov
2020-04-23 18:02                                                                         ` Nick Desaulniers
2020-04-23 18:27                                                                           ` Borislav Petkov
2020-04-27 11:37                                                                         ` [tip: x86/build] x86/build: Check whether the compiler is sane tip-bot2 for Borislav Petkov
2020-04-23 19:40                                                                       ` [PATCH] x86: Fix early boot crash on gcc-10, next try Kees Cook
2020-04-25  1:46                                                                       ` Arvind Sankar
2020-04-25  8:57                                                                         ` Borislav Petkov
2020-04-25 11:09                                                                           ` Jürgen Groß
2020-04-25 15:04                                                                           ` Arvind Sankar
2020-04-25 17:31                                                                             ` Borislav Petkov
2020-04-25 17:52                                                                               ` Borislav Petkov
2020-04-27 17:07                                                                                 ` David Laight
2020-04-25 18:37                                                                               ` Segher Boessenkool [this message]
2020-04-25 18:53                                                                                 ` Borislav Petkov
2020-04-25 19:15                                                                                   ` Segher Boessenkool
2020-04-25 22:17                                                                                     ` Borislav Petkov
2020-04-25 22:25                                                                                     ` Arvind Sankar
2020-04-17 10:38                                           ` [PATCH v2] x86: fix early boot crash on gcc-10 Peter Zijlstra
2020-04-18 13:12                                             ` David Laight
2020-04-17 10:41                                     ` Peter Zijlstra
2020-03-16 18:20         ` [PATCH] " Arvind Sankar
2020-03-16 18:54           ` Arvind Sankar
2020-03-16 19:53             ` Arvind Sankar
2020-03-16 20:08               ` Jakub Jelinek
2020-03-16 20:40                 ` Arvind Sankar
2020-03-16 22:12     ` Sergei Trofimovich
2020-03-17 11:46       ` Jakub Jelinek
2020-03-17 18:10         ` Sergei Trofimovich
2020-03-16 18:22 ` Arvind Sankar
2020-03-26 23:16 ` [PATCH v2] " Sergei Trofimovich
2020-04-27 11:37 ` [tip: x86/build] x86: Fix early boot crash on gcc-10, next try tip-bot2 for Borislav Petkov
2020-05-15 11:20 ` [tip: x86/urgent] x86: Fix early boot crash on gcc-10, third try tip-bot2 for Borislav Petkov

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